Gas or vapor phase particle production is an important technique for producing engineered nanoparticles. In a particle-producing reactor, basic product species are formed within extremely short time spans following ejection of a hot, reactive medium from an energy delivery zone. Following ejection from the delivery zone, further formation mechanisms determine the ultimate characteristics of the final product.
Although chemical reactions such as nucleation and surface growth within precursor materials occur largely during energy delivery, these formation mechanisms continue to be active in the first short moments following ejection. More prevalent in the post-ejection time period are bulk formation mechanisms such as coagulation and coalescence, which operate on already formed particles. Any proper conditioning of the hot, reactive medium following ejection from the energy delivery zone must account for these and other formation mechanisms to form a final product having desired characteristics. In some instances, maintaining a mixture at too high a temperature can lead to overly agglomerated particles in the final product.
In addition to particle formation, proper conditioning must account for post-formation processing of the product. Although particles, once formed, cool rapidly through radiative heat loss, the residual gas in which they are entrained after formation cools much more slowly, and especially so when confined. Confinement is necessary to some degree in any controlled-environment processing system, and economic concerns usually dictate relatively small, confining controlled environments. Therefore, such systems must provide efficient mechanisms for cooling of the entire gas-particle product, yet also provide for efficient transport of the product to collection points within the system.
Transport of particles within a gas stream relies on the entrainment of the particles, which is largely a function of particle properties, e.g., mass, temperature, density, and interparticle reactivity, as well as gas properties, e.g., density, velocity, temperature, density, viscosity, and composite properties, such as particle-gas reactivity. Cooling of a gas by definition affects gas temperature, but also may easily lead to changes in other properties listed above, exclusive of mass.
What is needed in the art is a method of and an apparatus for balancing efficient cooling and transport of a gas-particle product, which requires careful optimization of process parameters.